Process for Producing Articles From Ceramic or Metal by Electrophoretic Free Forming

ABSTRACT

The invention relates to an electrophoretic free forming process, by which both metallic and ceramic formed parts can be produced. In this process, a slip (suspension of water and metal powder or ceramic powder) is fed via a hollow needle ( 6 ) to the substrate ( 3 ) to be produced. By applying a voltage between the slip ( 7 ) and the substrate ( 3 ) a material deposit is produced. To build up a three-dimensional form scanned into a computer, the substrate is moved past the tip of the hollow needle ( 6 ) in a controlled manner. The control is performed on the basis of known CAD/CAM methods. With this process it is possible in particular to produce all formed parts known in dental technology on one machine. It is suitable in particular for producing reinforcing structures and for coating reinforcing structures with dentine or incisal material. Equally possible is the production of non-dental formed parts of dimensions comparable to those of dental formed parts.

This invention relates to a process for producing articles from ceramicor metal by electrophoretic free forming. The invention relates inparticular to producing dental parts. Dental parts in the context of theinvention are all dental parts that can be used in the prosthetic orconservative treatment of a patient, including frames for bridges,crowns for individual teeth, inlays, or dental prostheses coated withdentine and/or with incisal material.

Non-dental articles in the context of the invention mean all productsthat can reasonably be produced by electrophoresis based on theirdimensions and weight. As the term “free forming” itself implies, thesearticles are products that have a three-dimensional form. Not intendedare simple coatings that already have always been produced byelectrophoresis. Therefore, this process is particularly suitable forproducing components for precision mechanics that up to now have beenproduced by machining or casting.

Also, as far as the inventor knows, there is as yet no “electrophoreticfree forming process” in the sense of the invention.

The process according to the invention is based on the electrophoreticdeposition of solid particles from a slip. “Slip” in the context of theinvention means any suitable suspension of ceramic or metal powder in aliquid suspending medium.

Electrophoresis has gained sharply in importance in recent years for theproduction of wholly ceramic crowns and bridges. As representatives ofthis technology, the following publications are mentioned: WO 99/50 480A1, DE 100 21 437 A1, DE 101 27 144 A1, DE 103 39 603 A1, and WO 2004/041113 A1. Since one of the goals of these inventions is to produce whollyceramic dental prostheses, metals are intrinsically excluded as framematerials, especially since it could not be expected that metal powdercan be applied by electrophoresis, inasmuch as short circuits wouldprobably occur in the electrophoresis cell because of the conductivityof metals.

The presumed drawback also exists with this process, that ceramics suchas zirconium oxide, for example, which are subject to shrinkage uponsintering, are not satisfactorily processed since the ceramiccomposition is deposited on the working model. In the case of zirconiumoxide, therefore, a duplicate of the working model has to be made inthis process with expansion plaster. However, duplication implies anadditional source of error with regard to accuracy of form. Withalumina, on the other hand, best qualities are produced with the aboveprocess, including with respect to strength.

A process for producing dental parts from dental metal powder isdisclosed in the prior application DE 10 2005 052 113.4-23. The teachinggiven there with regard to slip composition and the sintering process isfully applicable to the present invention, so that both dental metal anddental ceramic can be processed with the present invention.

A generally known process for producing dental frames consists ofmilling out a frame from an isostatically prepressed block of ceramic,particularly zirconium oxide, using CAD/CAM technology. In this case,the dentition of the patient or a working model is scanned and the frameis milled on the basis of the scanned three-dimensional molding. Thisprocess makes it possible to compensate for the sintering shrinkage inthe case of zirconium oxide, but involves considerable milling expense.Another drawback consists of the fact that the accuracy of hollowcavities achieved from an impression on a working model cannot beobtained by milling. This is because the accuracy in internal milling islimited by the dimensions of the milling head. This process has thefurther drawback that an esthetically satisfactory dental prosthesiscannot be produced because of the uniformity of the ceramic block.

Therefore, it is the aim of the invention specified in Claim 1 todescribe a process for producing articles from ceramic or metal based onscanning technology that is substantially simpler than known scanningprocesses that is suitable for any material, and that has highdimensional accuracy.

Advantageous embodiments of the invention are described in the dependentclaims 1 to 10.

The invention is described below with reference to the production ofdental parts. However, it is obvious that non-dental articles can alsobe produced with the invention.

The Figures show:

FIG. 1 the principle of a machine for implementing the process;

FIG. 2 an enlarged section from FIG. 1.

In FIG. 1, 1 designates a computer that controls a CAD/CAM machine inaccordance with a scanned three-dimensional form. Corresponding machinesthat permit motion on 3 to 5 axes are already state of the art and neednot be described here in detail.

A substrate 3, in this case the frame of a three-membered bridgesupported by three pins 4, is shown on a bench 2. These pins can be partof the bench or can be applied by electrophoresis. The bench 2 can bemoved controllably around 5 axes.

Above the bench 2 is a slip feeder 5 that ends in a pointed feed element6 for the slip 7. A hollow needle such as those used in medicine asinjection needles has proved to be suitable for this. The slip can alsobe fed over the surface of a pointed feed element 6. With thisprocedure, it is recommended that the surface of the feed element beprovided with lengthwise profiling. It is important for exact operationthat the end of the feed element has no wide surface.

Another advantage could be produced by the feed element 6 rotatinggently. At the same time, it can exert a material-leveling function ifits end is designed like a mill.

The bench 2 is connected to the positive pole of an electrophoresiscontrol system 8, while the slip feeder 5 is at the negative pole. Tofacilitate the flow of slip in the needle 6, pressure is exerted on theslip 7 by a pressure device 9. In the embodiment shown, a piston is usedfor this purpose. A pressurized gas cushion would also be suitable.

As shown in particular in FIG. 2, the frame 3, already partiallyproduced, is fed past the tip of the needle 6 in accordance with thescanned program. The corresponding kinematically opposite process wouldalso be possible in principle by the needle 6 moving and the substratestanding still.

With a conventional slip, a voltage of about 40 V is applied, whichleads to a current up to about 100 mA. An electrophoretic effect thenoccurs, whereby deposition of the solid is produced directly beneath theneedle 6. In principle, it can be said that low voltage is used foraqueous slips because of gas evolution, while a higher voltage range isindicated for nonaqueous slips.

At the end of the deposition process, the blank has sufficient strengthto be sintered by known processes and infiltrated with glass ifappropriate.

The process pursuant to the invention is suitable for applying dentineor incisal material to the frame. For this purpose, the frame just hasto be fastened downward to the bench 2 with the recesses for the dentalstumps.

The device shown also has a mill 10 that is used to finish the partproduced if necessary. This is particularly the case when telescopecrowns or conical crowns that must have a smooth surface are being made.

Consequently, an electrophoretic free-forming process is made availablewith the invention that satisfies all requirements.

1. Process for the electrophoretic production of ceramic and metallicarticles, the process comprising the steps of providing a slipcomprising a suspension of ceramic or metal powder in a liquidsuspending medium, feeding the slip through a pointed feed element (6)onto a substrate (3) to effect a material deposition on the substrate,and applying a voltage between the slip (7) and the substrate (3),wherein the substrate (3) is moved past a tip of the feed element (6) ina controlled manner to construct a scanned three-dimensional form. 2.Process pursuant to claim 1, wherein the pointed feed element (6)comprises a hollow needle.
 3. Process pursuant to claim 1, wherein theslip comprises a metallic slip.
 4. Process pursuant to claim 1, whereinthe slip comprises a ceramic slip.
 5. Process pursuant to claim 1,wherein the substrate (3) is moved under control on the tip of the feedelement (6).
 6. Process pursuant to claim 1, wherein the process furthercomprises the production of frames.
 7. Process pursuant to claim 1,wherein a computer program in a computer (1) is provided and adapted tocompensate for sintering shrinkage.
 8. Process pursuant to claim 7,wherein the slip comprises a zirconium oxide slip.
 9. Process pursuantto claim 1, wherein dentine and/or incisal material is applied to thematerial deposition.
 10. Process pursuant to claim 2, wherein the slipis fed to the tip of the feed element (6) under pressure.
 11. Processpursuant to claim 1, wherein the feed element (6) comprises a pointedfeed element that has lengthwise profiling on the outside thereof. 12.Process pursuant to claim 1, wherein the feed element (6) rotates duringthe application of the slip.